Bethalto, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 8 °C (low) to 18.4 °C (high). Annual precipitation averages 1104.9 Millimeters. Bethalto is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.2 °C | 3.7 °C | 66.29 mm |
| February | -3.3 °C | 6.7 °C | 59.69 mm |
| March | 1.6 °C | 12.3 °C | 85.85 mm |
| April | 7.6 °C | 18.8 °C | 122.43 mm |
| May | 13.6 °C | 24 °C | 131.57 mm |
| June | 18.6 °C | 28.8 °C | 114.81 mm |
| July | 20.6 °C | 30.4 °C | 105.41 mm |
| August | 19.4 °C | 30 °C | 95.76 mm |
| September | 14.8 °C | 26.7 °C | 81.79 mm |
| October | 8.3 °C | 20.2 °C | 84.07 mm |
| November | 2.2 °C | 12.4 °C | 89.41 mm |
| December | -2.6 °C | 6.3 °C | 67.82 mm |
| Annual | 8 °C | 18.4 °C | 1104.9 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |